1. Field of the Invention
The present invention relates to a compressor as generally used in an air conditioning or cooling system to compress a refrigerant enclosed and circulating therein. More particularly, the invention is concerned with a device for protecting such refrigerant compressor against overheating, seizure and other troubles, being capable of detecting a critical loss of the refrigerant due to its possible leak from the refrigeration system by examining the refrigerant or compressor outer wall temperatures as monitored near inlet and outlet of the compressor against a specific relationship known between the inlet and outlet temperatures.
2. Description of the Prior Art
In a common mechanical compression refrigeration system, the refrigerant is circulated therein by a compressor repeating a refrigeration cycle wherein the refrigerant is condensed from a vapor state to a liquid state and the liquid refrigerant is then changed into a vapor while passing through an evaporator, removing heat from and thus cooling the surrounding air. The compressor is so connected to the refrigeration circuit as to admit the low-pressure vaporous refrigerant and discharge it after compression thereof to an elevated pressure.
In the event the refrigerant amount was decreased due to a leakage flow from the refrigeration circuit, the effect of the refrigerant to cool the compressor mechanism would be accordingly reduced, causing the compressor to be overheated, or even seized particularly in case the compressor uses a lubrication oil in the form of a spray mist to be contained in the refrigerant as a mixture. This is because the amount of lubricant to be delivered to the compressor is necessarily reduced as the amount of the refrigerant acting as an oil carrier is decreased.
To prevent such kinds of serious troubles occuring with the compressor, it has been considered necessary to monitor the refrigerant amount, and stop the compressor in the event the refrigerant amount falls below a predetermined lower limit. Hitherto, two common methods have been known to detect insufficiency of the refrigerant. The first of these is to monitor the refrigerant temperature which is known to rise in response to decrease of the refrigerant amount. The second method is to monitor the temperature of an oil pan provided in the bottom portion of the compressor.
Either of these methods indicated above, however, is not completely satisfactory in that the monitored temperature of the refrigerant or of the oil pan is not responsive accurately enough to faithfully reflect a reducing amount of the refrigerant. Thus, these proposed methods may often fail to detect a fall of the refrigerant amount below the predetermined minimum level, and are not effective enough to prevent the serious seizure trouble with the compressor.